Method for preparing a lithographic printing plate

1. A method for preparing a lithographic printing plate comprising the steps of:

imagewise exposing a lithographic printing plate precursor comprising a coating provided on a support having a hydrophilic surface, the coating containing thermoplastic particles and an infrared radiation absorbing dye characterized in that the coating further comprises a compound of formula IV:

wherein R 7 and R 8 are independently selected from the group consisting of a hydrogen, an optionally substituted alkyl group, an optionally substituted alkenyl group, an optionally substituted alkynyl group, an optionally substituted alkaryl group, an optionally substituted aralkyl group and an optionally substituted aryl or heteroaryl group; and

developing the exposed precursor in a gum solution.

2. The method according to claim 1 , wherein the infrared radiation absorbing dye contains a substituent selected from bromo and iodo.

3. The method according to claim 2 , wherein the infrared radiation absorbing dye has a structure according to Formula V;

wherein

Z and Z′ represent —S—, —CR a R b — or —CH═CH—;

A represents hydrogen, an optionally substitued alkyl, aralkyl or aryl group, halogen, —OR c , —SR d , —SO 2 R e , —NR f R g , —NR h (SO 2 R i ) or —NR j (CO 2 R k ) wherein R c represents an optionally substituted aryl group, R d represents an optionally substituted alkyl, aralkyl, aryl or heteroaryl group, R e represents an optionally substituted alkyl, aryl, or heteroaryl group, R f represents an optionally substituted alkyl, aralkyl or aryl group, R g represents an optionally substituted aryl group, R h represents an optionally substituted alkyl or aryl group, R i represents an optionally substituted alkyl or aryl group or —NR i1 R i2 wherein R i1 and R i2 represent hydrogen, an optionally substituted alkyl or aryl group, R j represents an optionally substituted alkyl or aryl group;

T and T′ independently represent hydrogen, alkyl, alkoxy, cyano, —CO 2 R k , —CONR l R m , —SO 2 R n , —SO 2 NR o R p or an annulated benzo ring wherein R l , R m represent hydrogen, an optionally substituted alkyl or aryl group, R n represents an optionally substituted alkyl or aryl group and R o and R p represent hydrogen, an optionally substituted alkyl or aryl group;

R 9 and R 10 represent the necessary atoms to form a ring;

n represents an integer ranging from 0 to 3;

X represents —CH 2 —, —O— or —S—;

M + represents a counterion to balance the charge.

4. The method according to claim 1 , wherein the infrared radiation absorbing dye has a structural element according to Formula VI;

wherein

B represents hydrogen, halogen or a monovalent organic group;

Y and Y′ independently represent —CH— or —N—;

R 11 and R 12 independently represent hydrogen, an optionally substituted alkyl or aryl group or represent the necessary atoms to form a ring;

* represent the linking positions to the rest of the molecule.

5. The method according to claim 1 , wherein the thermoplastic particles have an average particle diameter, measured by Photon Correlation Spectrometry, between 20 and 55 nm.

6. The method according to claim 1 , wherein the developing step is carried out off press in an automated processing unit comprising rotating brushes.

7. The method according to claim 2 , wherein the thermoplastic particles have an average particle diameter, measured by Photon Correlation Spectrometry, between 20 and 55 nm.

8. The method according to claim 3 , wherein the thermoplastic particles have an average particle diameter, measured by Photon Correlation Spectrometry, between 20 and 55 nm.

9. The method according to claim 2 , wherein the developing step is carried out off press in an automated processing unit comprising rotating brushes.

10. The method according to claim 3 , wherein the developing step is carried out off press in an automated processing unit comprising rotating brushes.